Multifocal motor neuropathy as a mimic of amyotrophic lateral sclerosis: Serum neurofilament light chain as a reliable diagnostic biomarker

Introduction/Aims: The clinical presentation of multifocal motor neuropathy (MMN) may mimic early amyotrophic lateral sclerosis (ALS) with predominant lower motor neuron (LMN) involvement, posing a diagnostic challenge. Both diseases have specific treatments and prognoses, highlighting the importance of early diagnosis. The aim of this study was to assess the diagnostic value of serum neurofilament light chain (NfL) in differentiating MMN from LMN dominant ALS. Methods: NfL was measured in serum in n = 37 patients with MMN and n = 37 age- and sex-matched patients with LMN dominant ALS, to determine the diagnostic accuracy. Clinical and demographic data were obtained at the time of NfL sampling. Results: Serum NfL concentration was significantly lower in MMN patients compared to ALS patients (mean 20.7 pg/mL vs. 59.4 pg/mL, p < .01). NfL demonstrated good diagnostic value in discriminating the two groups (AUC 0.985 [95% CI 0.963-1.000], sensitivity 94.6%, specificity 100%, cut-off 44.00 pg/mL). Discussion: NfL could be a helpful tool in differentiating MMN from LMN dominant ALS in those patients in whom electrophysiological and clinical examinations remain inconclusive early in the diagnostic process.